It's something to do with the Spirit World. That's about all I know. I don't think anyone has figured it out beyond that, but you're not the first person I've met today that's from a different time or place. Avatar Aang isn't either.

I'm not even from this time. I arrived in the same way about a week or so ago. I've just had more time to figure out what I can than most of the people showing up today.